Investigation of multiferroic magnetic systems by ultrasonic velocity measurements

我们主要对同时具有反铁磁性、铁电性和铁弹性的多铁化合物的研究感兴趣。除了基本的科学兴趣之外，这类磁电材料（显示其磁性和铁电性质之间耦合的材料）可能被用作未来电子存储设备中控制磁化的替代手段，以及致动器，开关和磁场传感器。对这一领域的兴趣是由最近的结果引发的，这些结果表明三角形晶格反铁磁体，由于磁挫折而有利于非共线自旋构型，是观察强磁电效应的良好候选者。因此，本研究计划的目的是研究在CuO （T = 230 K）和BiFeO3 （T = 643 K）的低温甚至高温下螺旋磁结构稳定后显示铁电性的一系列受挫多铁化合物的磁性、铁电性和弹性。这类材料的基本弹性特性是通过高分辨率超声速度测量获得的。我们的实验室提供了一种灵活的方法来研究温度和磁场作用下单晶的弹性特性。我们是世界上为数不多的能够在宽范围内（2 - 300 K， 0 - 15 Tesla和0 - 15 kbar）测量弹性特性和相图作为这三个外部参数的函数的团队之一。我们的方法具有获得重要结果的潜力，以澄清在该化合物家族中观察到的弹性，电和磁性之间耦合的性质。这些结果也将为本课题组开发的理论模型提供指导。因此，这项工作将有助于更好地理解磁电化合物的性质，并可能导致技术应用新材料的开发。

We are principally interested in the study of multiferroic compounds which are simultaneously antiferromagnetic, ferroelectric, and ferroelastic. Besides the fundamental scientific interest, this class of magnetoelectric materials (materials that show a coupling between their magnetic and ferroelectric properties) can potentially be used as an alternative means for controlling the magnetization in future electronic memory devices, as well as for actuators, switches, and magnetic field sensors. The interest in this field has been trigger by recent results which suggest that triangular lattice antiferromagnets, which favour non-collinear spin configuration due to magnetic frustration, are good candidates for the observation of strong magnetoelectric effects. Thus, the objective of this program of research is to investigate the magnetic, ferroelectric, and elastic properties of a series of frustrated multiferroic compounds which display ferroelectricity induced upon the stabilization of a helical magnetic structure at low or even high temperatures in the case of CuO (T = 230 K) and BiFeO3 (T = 643 K).The fundamental elastic properties of this class of materials are accessed using high resolution ultrasonic velocity measurements. Our laboratory offers a flexible way to investigate the elastic properties of single crystals under hydraulic pressure as a function of temperature and magnetic field. We are one of the few groups in the world capable of measuring elastic properties and phase diagrams as a function of these three external parameters over a wide range (2 - 300 K, 0 - 15 Tesla, and 0 - 15 kbar). Our approach holds potential for the acquisition of significant results in order to clarify the nature of the coupling between elastic, electric, and magnetic properties observed in this family of compounds. These results will also provide guidance for theoretical models developed by our group. This work should therefore contribute to a better understanding of the properties of magnetoelectric compounds and could lead to the development of new materials for technological applications.